1. Field of the Invention
This invention relates to curtain wall systems, specifically an improvement on curtain wall systems utilizing multiple framed panels with various facing materials, e.g., as described by Ting in U.S. Pat. Nos. 5,452,552 and 5,598,671. The structure disclosed in U.S. Pat. No. 5,452,552 is also known as an exposed frame airloop curtain wall system and the structure disclosed in U.S. Pat. No. 5,598,671 is also known as a hidden frame airloop curtain wall system.
2. Description of the Prior Art
In addition to providing an aesthetic appearance for the sides of a modern multi-story building, some of the major performance objectives of a curtain wall system of supported panels are as follows:
(1) to provide a barrier or at least resistance to excessive amounts of exterior air infiltrating around the edges of panels into one or more interior environments within the building;
(2) to provide a barrier or at least resistance to excessive amounts of exterior rain or other exterior liquids/particles infiltrating around the panel edges into one or more interior spaces within the building, typically when the liquids or particles tend to infiltrate in conjunction with air infiltration;
(3) to provide resistance to structural loads, specifically including supporting the weight of the panels and resisting seismic loads, wind loads, and thermal expansion/contraction loads, if any; and
(4) to provide a thermal barrier or at least resistance to excessive heat transfer between the exterior air and one or more interior environments.
The two aforementioned U.S. Patents are primarily directed to solving problems with excessive air and water infiltration or leakage using an airloop system. Previous designs dealing with water leakage typically required a nearly perfect seal to stop excessive air and water infiltration. The aforementioned U.S. Patents describe a pressure equalized airloop having two seals that separate the functions of sealing water and air, providing acceptable air and water infiltration rates even with imperfect seals. In addition, one embodiment of the airloop system allows panels to be shop assembled with perimeter panel frame extrusions so that a more reliable seal can be fabricated and a pressure equalized inner airloop is formed along the facing panel frame edges. A pressure equalized outer airloop is formed after field erection of the panels with bordering panel frames.
However, the prior airloop systems described can still allow, e.g., under extreme dynamic wind conditions, rain water to get to the air seal. Since the air seal in the airloop system can be assumed to be imperfect, water leakage can occur. In addition, the panel securing fasteners in the airloop systems described in U.S. Pat. Nos. 5,452,552 and 5,598,671 would be put in tension under negative wind load conditions (e.g., winds and/or wind loads directed away from the building interior on one side of the building) such that the connection strength and seal compression may be reduced. Still further, repeated negative wind loads could cause the securing screws to become loosened or stretched, causing the danger of one or more panels to fall off the building.
In addition, the panel frames may not provide the desired thermal insulation for some applications. Still further, seismic and other loads may tend to crack or loosen panels and damage seals if the building structure is even slightly deformed. Thus, although significant advancements have been made in achieving some objectives for a curtain wall system, specifically including the two aforementioned patents, an improved system is still needed.